The warnings follow the inconclusive results of this weekend's peace talks in Congo, which have left rebel leader Laurent Kabila free to go ahead with his threat to capture the capital by force. The advance rebel units are believed to be within 100km of the capital, having moved 300km since capturing the city of Kikwit a week ago. Reports in Kinshasa say that rebel radio is claiming some of Mr Kabila's fighters have already infiltrated the capital in civilian clothes.
Speaking in his southern base of Lubumbashi, Mr Kabila has given President Mobutu Sese Seko three days to resign unconditionally or else "perish with his power".
Mobutu aides yesterday rejected this ultimatum, describing it as the "words of a hoodlum".
The US ambassador to the United Nations, Bill Richardson, visited Mr Kabila in Lubumbashi yesterday in a last ditch effort to persuade him to pursue his objectives by peaceful means.
The drive on Kinshasa comes despite Sunday's face-to-face meeting between Mr Mobutu and Mr Kabila, which took place aboard the South African naval supply ship Outeniqua at Pointe-Noire in the Congo. Although Mr Mobutu has agreed in principle to step down as President, thereby fulfilling the rebels' avowed war aim, hopes for an immediate end to the conflict proved groundless when the two men failed to agree on how and when this should happen.
According to a communique released after the meeting, Mr Mobutu wants to remain head of state during a transition period leading to elections. Mr Kabila refused to accept anything less than Mr Mobutu's immediate resignation and says his Alliance of Democratic Forces for the Liberation of Congo- Zaire should manage power during the transition period.
The chairman for the talks, South Africa's President Nelson Mandela, said he plans to bring both sides back together next week for further talks. In the meantime, he made it plain, there was little prospect of a ceasefire - "Ceasefire is not in Mr Kabila's vocabulary," he remarked.
Life went on much as normal in Kinshasa yesterday, despite the growing prospect of a rebel attack. Most Kinshasans now say they would welcome Mr Kabila's rebels to their city. After 32 years of corrupt and incompetent rule the ailing President Mobutu is deeply unpopular, and few people now fear to say so.
Many observers in the capital believe that, in the absence of a ceasefire, it will fall in the next few days, possibly without a major battle. The rebels have encountered only light resistance from the government's undisciplined army in their long march from the east, and there is little sign that the army is prepared to put up a real fight now.
The government claims to have launched a counter offensive, with elements of the elite Presidential Security Detachment (ESP) which it says is holding the rebels along a 60km wide front. No apparent effort has been made to fortify key installations around the capital, and no curfew has been imposed.
Many Zaireans fear that the main threat to their safety comes not from the rebels but from the government army, which has a long tradition of violence against it's own people.
Across the Congo river in Brazzaville several thousand troops from the US, France, Britain and Belgium are on standby to evacuate foreign citizens in the event of an attack.